The present invention relates to a large-sized float with wave-resistant properties (hereinafter referred to as xe2x80x9cwave-resistant mega-floatxe2x80x9d), such as a large-sized floating structure, a floating bridge, floating warehouse, etc., floating on the ocean, the fluctuation of the mega-float due to incident waves being reduced.
Development of mega-floats floating on the ocean has been promoted. A conventional mega-float is a box-shaped floating structure disposed in a calm sea area created by a stationary breakwater. The floating structure includes a plurality of sealed floating chambers and has a flat deck and a flat bottom.
Mega-floats are thus applicable to various purposes, for example, offshore airports (including offshore heliports), offshore plant barges and, prospectively, offshore cities.
FIG. 1 shows a mega-float provided with a stationary breakwater. A stationary breakwater b is set on a seabed a, thereby creating a calm sea area c. In addition, a mega-float e is floated in the calm sea area c. Mooring-posts d are provided so as to surround the mega-float e. The mega-float is moored to the mooring-posts d via dampers f. The mega-float e has, for example, a length of 1500 m, a width of 500 m, a thickness of 7 m and a draft of 2 m. The thickness of the mega-float e is less than the length thereof.
Analytic calculations were conducted for elastic response in waves at a depth of 20 m, with the direction of waves, the cycle of waves and the flexural rigidity of mega-float e being systematically varied. It was found that design specifications are not satisfactory even when the limit wave height is 2 m.
If the depth of water increases, the cost for installing the stationary breakwater b becomes very high. If the stationary breakwater b is replaced with a floating breakwater, approach to the pier or stevedoring becomes difficult. Under the circumstances, there is a demand for mega-floats which require neither stationary breakwaters or floating breakwaters.
In order to dispense with the stationary breakwater b or the floating breakwater without increasing the cost or adversely affecting vessels, etc., it is necessary to provide the mega-float e itself with a fluctuation reducing means, thereby enhancing wave-resistant properties. According to one possible method, a wave-damping structure is added to that side portion of the mega-float e, which is located upstream in a direction in which waves travel, thereby reducing incoming waves to the mega-float e. In the prior art, as shown in FIG. 2, a wave-damping structure g is fixed to a front end portion h of the mega-float e, which is located upstream in the direction from which waves travel.
The conventional wave-damping structure g is devised by utilizing a mechanism for reflecting, scattering or breaking waves. There types of the structure g are publicly known: a curtain wall type structure (FIG. 3A); an open tank-plate type structure (FIG. 3B); and an (immersed) beach type structure (FIG. 3C).
The curtain wall type structure is effective only to short-wavelength components. The open tank-plate type structure or beach type structure gradually breaks the waves, and are thus effective to both short- and long-wavelength components. Experimental data, however, shows that a considerable length (e.g. about ⅓ of the wavelength) is necessary in order to obtain a sufficient wave-damping effect. If the wavelength is 200 m, the length of the structure needs to be 70 m to 80 m, resulting in an increase in size and cost.
The present invention has been made in consideration of the above circumstances and its object is to provide a wave-resistant mega-float capable of efficiently damping waves with a simple-structured wave-damping member provided on the mega-float and reducing fluctuation due to wide-range wave cycles and high waves, without installing a stationary breakwater, etc.
In order to achieve the object, according to a first aspect of the invention, there is provided a wave-resistant mega-float comprising:
a first flat plate provided on a front end portion of a large-sized floating body, penetrating a water surface, and extending downward below a bottom surface of the floating body, the front end portion of the floating body being located on an upstream side in a direction from which waves travel; and
a second flat plate attached to a lower end portion of the first flat plate such that the second flat plate extends toward the upstream side.
With this invention, as will be described later in detail, when waves come in from the upstream side while the mega-float floats on the sea, a fluctuating pressure on the immersed horizontal plate of the wave-damping member (second flat plate) (with a value obtained by subtracting a pressure on the upper surface of the immersed horizontal plate from a pressure on the lower surface of the plate) and a fluctuating pressure on the bottom surface of the front end portion of the mega-float have opposite phases and cancel each other. Consequently, a pressure integration value of wave (wave force) acting on the front end portion of the mega-float decreases and the fluctuation can be reduced.
According to a second aspect of the invention, there is provided a wave-resistant mega-float comprising:
a first flat plate provided on a front end portion of a large-sized floating body, penetrating a water surface, and extending downward below a bottom surface of the floating body, the front end portion of the floating body being located on an upstream side in a direction in which waves travel; and
a second flat plate attached to a lower end portion of the first flat plate and extending toward the upstream side in an inclined downward direction.
With this invention, as will be described later in detail, when waves have come in from the upstream side while the mega-float floats on the sea, a fluctuating pressure on the immersed horizontal plate of the wave-damping member (second flat plate) (with a value obtained by subtracting a pressure on the upper surface of the immersed horizontal plate from a pressure on the lower surface of the plate) and a fluctuating pressure on the bottom surface of the front end portion of the mega-float have opposite phases and cancel each other. Consequently, a pressure integration value of wave (wave force) acting on the front end portion of the mega-float decreases and the fluctuation can be reduced.
According to a third aspect of the invention, there is provided a wave-resistant mega-float comprising:
a first flat plate provided on a front end portion of a large-sized floating body, which front end portion is located on an upstream side in a direction from which waves travel, the first flat plate extending toward the upstream side;
a second flat plate attached to the first flat plate, the second flat plate penetrating a water surface and extending downward below a bottom surface of the floating body; and
a third flat plate attached to the second flat plate and extending toward the floating body.
With this invention, as will be described later in detail, when waves have come in from the upstream side while the mega-float floats on the sea, a fluctuating pressure on the immersed horizontal plate of the wave-damping member (second flat plate) (with a value obtained by subtracting a pressure on the upper surface of the immersed horizontal plate from a pressure on the lower surface of the plate) and a fluctuating pressure on the bottom surface of the front end portion of the mega-float have opposite phases and cancel each other. Consequently, a pressure integration value of wave (wave force) acting on the front end portion of the mega-float decreases and the fluctuation can be reduced.
In the above inventions, an extension deck extending toward the upstream side from the upper end of the first flat plate may be provided. Thereby, the area of the deck of the mega-float can be increased and vessels, etc. are prevented from colliding with the immersed horizontal plate provided on the front side of the mega-float.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.